The objective of this project is to contribute to more detailed understanding of the electronic structure of the class of porphyrin molecules. Spectroscopic experiments are planned in which free base and metal complexes of porphin are incorporated as guest molecules into crystalline aromatic hosts. High resolution low temperature optical spectroscopy, selective excitation spectroscopy, and electron spin resonance techniques will be used in the study of these single crystal specimens. New features of this research are 1) use of crystalline hosts to obtain polarized sharp line optical absorption spectra and 2) use of tunable dye laser in selective excitation experiments to study the nature of the multiple structure observed in sharp line porphyrin spectra. These experiments will provide stringent and comprehensive tests of current theory and, in particular, resolve a possible conflict reported by this laboratory between experiment and theory of free base porphyrin spectra.